Electric furnace



Feb. 20, 1934. w RE 1,947,612

ELECTRIC FURNACE Original Filed Oct. 24, 1931 Fg z Elmo/whorl I Nov/ePatented Feb. 20, 1934 PATENT OFFICE ELECTRIC FURNACE William a. mom,Pittsburgh, Pa, assignor to Pittsburgh Research Corporation, Pittsburgh,

Original application October 24, 1931, Serial No. 570,957. Divided andthis application May 10, 1932. Serial No. 610,441

9Clalms.

My invention relates to improvements in electric furnaces and moreparticularly to furnaces adapted for annealing or similar heat treatingoperations.

l An important object of my invention is the provision of a novelresistor support for use in this type of furnace.

Another object of my invention is to provide a novel and efilcientdistribution of the resistor elements about the walls of the furnace.

Other objects and advantages of my invention will be apparent during thecourse of the following description.

This is a division of my co-pending application 570,957 for electricfurnaces filed October 24, 1931. V

In the accompanying drawing, which forms a part of this specification,and wherein like characters of reference denote like or corre spondingparts throughout the same,

Figure 1 is a diagrammatic elevation of one of the side walls of myfurnace showing the distribution of resistor elements thereon,

Figure 2 is a similar view of one of the end walls of the furnace,

Figure 3 is a perspective view showing the resistor element mounted onits supports,

Figure 4 is a vertical sectional view through the resistor support,

.Figure 5 is a similar view of a slightly modified form of resistorsupport, and,

. Figure 6 is a detail of the resistor supporting spool showing twoforms thereof.

In the drawing, wherein for the purpose of illustration is shown apreferred embodiment of my invention, the numeral 10 designates aheating furnace or hood of any suitable construction and having electricresistance elements 44 therein. I

In the heat treating of material piled vertically on the hearth of thistype of furnace, if the heater elements are uniformly distributed overthe wall surfaces the upper parts of the charge will attain a highertemperature than the lower parts of the charge due to the effect ofconvection and re-radiation from the arched roof and other factors.Heretofore it has been the practice to avoid this overheating of the topof the furnace by the use of two or more zones of heater elements eachseparately controlled so that the ribbons in the higher zones arecarried at a lower temperature than ribbons in the lower zone tocompensate for this tendency to overheating of the top of the furnace.Such an arrangement is disadvantageous, however,

and I propose to obtain uniform heating of the charge by a noveldistribution of a single zone of heating elements. a

An ordinary and advantageous use of my invention is for heat treatingsheets of metal 50 stacked horizontally on the furnace base with theedges to the side-walls. The heat conductivity of such charge is verymuch greater horizontally than vertically, and for that reason Ipreferably place my heating elements principally on the side walls ofthe furnace with a small portion on the end walls to compensate forequal heating there. I also preferably locate the major portion of theresistors of the heating elements below the horizontal center of thecharge so that the radiation and convection had of the charge isapproximately the same in the bottom portions of the charge and the topportions of the charge. I also prefer to so distribute the heat on theside-walls to avoid overheating the corners. Irregular heating tends tobuckle the sheets or over-oxidize the edges of the corners which by myinvention I have avoided.

- In Figure 1 I have shown one method of accomplishing this result. Theheating element in the form of a resistor ribbon 44 is supported bysuitable insulating supports 45 arranged in upper, lower and middlerows. In the arrangement shown in Figure 1, for every resistor loop thatextends from the lower to the upper row of supports, two loops extendonly to the middle row of supports. As a consequence, over two thirds ofthe heating element surface'is arranged below the horizontal center lineof the furnace. It is obvious that other arrangements of the resistorloops may be used to obtain the desired distribution.

The usual practice is to use the same proportion of heating elements onthe end walls as on the side walls but this has been found to beimpracticable, due to overheating of the ends of the charge in this typeof furnace. If any appreciable amount of heat is supplied by the endwalls, the end portions of the charge are sup- 0 plied with heat fromthree sides, whereas the central portions of the charge are suppliedwith heat from only two sides, resulting in very unequal heating of thecharge. To remedy this defect, I propose to heat'the charge from twosides only and produce at the end walls only enough heat to compensatefor the heat losses of the end walls. This is accomplished by providingonly a few resistorloops on the end walls, as seen in Figure 2 where theloops are arranged in no the center and at the bottom of the end wallswhere most of the heat losses occur. Any desired distribution could beused, however.

In Figures 3, 4, 5 and 6 I have shown a resistor support which is welladapted for this type of furnace. Insulating and refractory blocks 46are set into the walls of the furnace cover and carry heat resistantmetal pins 47 which project beyond the inner surface of the furnacecover and slidably receive electrical insulating spools 48 which areheld in place by suitable fasteners such as U-shaped clips 49 fitting insuitable notches in the ends of the pins 47. In the form of theinvention shown in Figures 3 and 4, the block 46 is split horizontallyand provided with a bore to receive the pin and communicating with avertical bore 50. The pin 47 is provided with a bent end which extendsinto the bore 50 to prevent removal of the pin when the block sectionsare assembled. Additional bores 51 may be provided for securing theblock sections together or to receive the pin if a different position ofthe pin is desired.

The spool may be formed in one piece as shown in Figure 5 and at theright of Figure 6, or it may be split at its center to facilitateassembling, as seen in Figure 4 and at the left of Figure 6. The centerportion of the spool is polygonal in cross section to present knife edgecontacts to the resistor ribbon, and thereby reduce conduction losses tothe support and permit a less hampered radiation from the resistor.

It will be seen that the spools 48 may be readily removed or replaced,by removing the fastener 49 and sliding the spool from the pin, withoutremoving the block 46 from the wall.

In Figure 5 the insulating block 46' is formed in one piece and a lagscrew 47' is used in place of the pin 47. The screw 47' may be removedand replaced without removing the block 46 from the wall. The head ofthe screw 47' retains the spool in position.

While I have shown and described the preferred embodiment of myinvention it is to be understood that various changes in the size, shapeand arrangement of parts may be resorted to without departing from thespirit of my invention or the scope of the subjoined claims.

Having thus described my invention what I claim and desire to protect byLetters Patent is:

1. In a heat treating furnace, resistance element supports arranged inthree spaced substantially horizonal rows about the walls of said fur-'nace, and a resistance element looped about said supports, and extendingfrom the bottom row of supports to the intermediate and top rows ofsupports, some of the resistance loops terminating at the intermediaterow of supports, whereby a greater part of the heating surface of saidresistance element is arranged below the horizontal center of the chargeof said furnace.

2. The method of heating a charge of material in a closed space whichconsists in heating from two opposite sides of the material, andcompensating for heat losses on the other sides of the material.

3. A resistance support for electric furnaces comprising a pin securedto the furnace wall,

and an insulating spool removably arranged on said pin, said spool beingsplit intermediate its ends.

4. A resistance support for electric furnaces comprising a pin securedto the furnace wall, and an insulating spool removably arranged on saidpin, said spool having its intermediate portion polygonal in crosssection, and being split intermediate its ends.

5. The method of heating a charge of material in a closed space whichconsists in heating from two opposite sides of the material, andcompensating for heat losses on the other sides of the material, whilesupplying the greater portion of heat below the horizontal center of thecharge.

6. In a heat treating furnace, a resistance element supported in loopswhich extend from points adjacent the bottom of the furnace towards thetop thereof, some of the loops extending to points adjacent the top ofthe furnace while other of said loops terminate at points adjacent thehorizontal center of said furnace whereby the greater portion of theheating surface of said resistance element is arranged below thehorizontal center of the charge in said furnace.

'7. In a heat treating furnace, a resistance element supported in loopsof varying lengths in said furnace, the greater portion of the heatingsurface of said resistance element being arranged below the horizontalcenter of the furnace.

8. In a heat treating furnace having a generally rectangular shape, aresistance element arranged about the four walls of the furnace, therebeing a greater amount of the heating surface of the resistance elementon the side walls per unit wall area than on the end walls of thefurnace.

9. In a heat treating furnace having a gen erally rectangular shape, aresistance element arranged in loops upon the walls of the furnace,there being a greater portion of the heating surface of the loops belowthe horizontal center of the furnace than above it, and there being .agreater amount of the heating surface of the resistance element on theside walls per unit wall area than on the end walls of the furnace.

WILLIAM E. MOORE.

